Series-connected Valve Regulated Lead Acid Batteries (VRLA) are adopted as batteries of standby power supply in the fields such as power generation, power supply and communication. When Alternating Current (AC) power supply has a failure, the standby power supply must supply uninterrupted power at once to guarantee the normal operation of the whole system. Therefore, it is very important about how to judge that whether battery has good power supply ability or not for reliability and security of the above mentioned fields. Since VRLA battery is hermetically sealed, the internal material can not be detected with a visual method. However, the power supply ability of battery can be estimated well through detecting battery internal resistance. Generally, if battery internal resistance is 25% more than the average value of internal resistance of the storage battery, power supply ability of the battery is already decreased, it should be mainly monitored; if battery internal resistance is 50% more than the average value of internal resistance of the storage battery, power supply ability of the battery is not reliable, it should be replaced. Since the value of battery internal resistance is extremely little, for example, the internal resistance range of widely used 100-4000A VRLA battery is about 1.5-0.06 mΩ, and the battery of standby battery is commonly on a floating charge state, charge current provided by a rectifying circuit in a battery charger imposes large interference signals on two ends of the battery, and to guarantee the reliability of the standby power supply, the cable connecting to the battery can absolutely not be cut off to measure resistance, on-line resistant measurement can only process in a strong interference environment of battery floating charge, this causes a big problem for detection of battery power supply ability.
CN patent application No. 200520100597.3 discloses a battery on-line monitoring system. This system includes a monitoring computer which is used to connect sectional tap of storage battery to an internal resistance load module and a battery voltage detection module used to alternative discharge, the computer connects sectional tap of storage battery through the internal resistance load module, each sectional storage battery following the tap is alternatively discharged, the battery voltage detection module is used to collect discharge and recovery voltage curves of each battery, and thereby the internal resistance of each battery is calculated. However, this disclosed system only simply introduces the connection relationship among each part, the principle and concrete steps are not sufficiently disclosed, it can not understand and evaluate the system. CN patent application No. 200520133538.6 discloses an on-line monitoring system for battery internal resistance and deterioration state, the invention mainly sets sectional points in storage battery, and there is no specific description for the concrete measurement circuits for each battery, it can not understand and evaluate the system as well.